Reciprocating piston and cylinder air motors have been in use for well over the past 100 years to drive material handling pumps, power tools and many other uses as a prime mover. These piston and cylinder motors are single acting or double acting. In single acting piston and cylinder devices fluid under pressure is ported selectively to only one side of the piston in a forward stroke, and the piston is returned by non-fluid pressure means, such as a return spring.
In double acting piston and cylinder motors, fluid under pressure is ported into one side of the piston to drive it in a forward stroke and alternately to the opposite side of the piston to drive it in a return stroke. Usually a main directional valve is provided for porting fluid under pressure from a source alternately to two main passages connected to the opposite ends of the piston and for porting fluid from the unpressurized main passage to exhaust.
Noise attenuation has always been a problem with high pressure reciprocating piston air motors because exhaust air blasting from the motor can create a deafening roar that is objectionable and sometimes harmful to workers in the area. For example, sound levels in excess of 90 dBA (sound pressure level measured in A-scale decibels) for a period of eight hours or more is generally considered excessive and, therefore, in need of attenuation. Noise can be attenuated by the use of sound-absorbing materials in the work place, barriers between the sound generator and working personnel, or a muffler at the source. Mufflers have been the most popular technique for reducing noise levels to acceptable values, and for the most part, these include canister-type devices mounted externally to the piston and cylinder air motor that receive exhausting air and decrease the velocity and expand the air before final exhaust from the muffler into the work area. These mufflers achieve velocity deceleration and expansion in a variety of manners, including expansion chambers and flow-stream direction changes with baffling deflectors, and filtering material.
The problem with these mufflers is that because most of them require expansion chambers, they are quite large, and in some cases almost as large as the air motor itself. Frequently these mufflers use filtering techniques that also require periodic cleaning. The size of the muffler and the complexity of the filtering or baffling system make it, unfortunately, a major contributor to the cost of piston and cylinder air motors.
It is a primary object of the present invention to ameliorate the above-noted problems in reciprocating piston pneumatic motor sound attenuation systems.